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We propose and demonstrate a selectively microfluidic-infiltrated method for the group birefringence regulation in a microstructured optical fiber. Meanwhile, an Optical Frequency Domain Reflectometry (OFDR) with an equivalent resolution of 0.6 Hz or 10-6 RIU is utilized to characterize its polarization separation and group birefringence change. By selectively infiltrating a fluid with a high thermal-optic coefficient into twin air holes nearby the silica fiber core, tunable group birefringence is observed and measured by polarization separation in beat frequency domain. Moreover, due to the co-effects of the filled and unfilled fiber segments, the twin critical zeros of the overall group birefringence are observed at 16.5 and 43.0, respectively. The unique position exchange of LP01x and LP01y presents at the twin critical zeros, which is investigated via the OFDR technique as well. Therefore, by combining the unfilled fiber segment with negative group birefringence and filled fiber segment with positive group birefringence, dual zeros in group birefringence are achieved with position exchange of the LP01x and LP01y peaks in beat frequency domain. Our demonstration provides potentials in flexible regulation and real-time observation of the group birefringence in microstructured optical fiber.

Sunlight Concentrated and transmission for daylighting via optical fibers is a booming technology of direct utilization of solar energy. It uses optical fibers to introduce sunlight deep into building interior. In this work, a sunlight concentrating and transmitting system via plastic optical fibers was developed and tested. This study addressed the cooling problem of the plastic optical fibers under highly irradiation. Polymethylmethacrylate (PMMA) plastic fibers have a strong absorption effect on infrared light, which means that plastic fibers heat up so much when they transmit focused sunlight that they burn. In this study, a comprehensive cooling approach was developed to solve the overheating problem of plastic optical fibers, which consists of an infrared filter, cooling water and a homogenizer. The transmission efficiency of the system was measured to be about 15%. Experiments show that the comprehensive cooling measures developed can ensure that PMMA plastic optical fibers are in a safe temperature range. This shows that it is feasible to use low-cost plastic optical fibers instead of expensive silica fiber to transmit high flux for daylighting.

In this paper, we have proposed an etched silica Fiber Bragg Gratings (FBGs) based interrogation technique using an optical spectrum analyser (OSA). The efficiency of the proposed system has extensively been investigated for measuring the temperature and strain simultaneously with higher sensitivity and accuracy covering a larger measurement range. A Single mode-Multi mode-Single mode fiber (SMS) which acts as a bandpass filter is employed in the circuitry for an efficient and fast interrogation technique. We recorded a remarkable enhancement in sensitivity of 20.30 pm/°C and 2.89 pm/μɛ over the temperature and strain range of 25–225 °C and 50–2050 μɛ, respectively. These data were recorded with the strain resolution of ±10 μɛ whereas the resolution for the temperature is ±0.50 °C. The experimental results show the capability of the sensor for measuring the strain and temperature simultaneously with higher intrinsic sensitivity and resolution. The performance of the proposed sensor has been compared with various reported techniques.

We presented a hybrid sapphire dual-Fabry—Perot- cavities sensor for high temperature and refractive index measurement. A double-sided polished sapphire solid wafer is connected in series with a double-sided parallel sapphire C-ring and a single-sided polished sapphire mirror to form the hybrid Fabry—Perot interferometer. The double-sided polished sapphire solid wafer acts as the first Fabry—Perot cavity for temperature sensing, and the sapphire hollow C-ring cavity constitutes the second Fabry—Perot cavity for measuring the refractive index of external environment medium. The single-sided polished sapphire mirror serves as the most distal reflector. Heterogeneous fiber splicing between sapphire fiber and multimode silica fiber is realized to achieve long-distance transmission of interference signals. A series of high temperature measurement experiments range of room temperature to 1080 °C in an air environment and refractive index measurement experiments in a liquid environment were carried out. Based on the changing rates of corresponding Fabry—Perot cavity optical path difference against refractive index and temperature, we calculated the sensitivities of the sensor. The refractive index and temperature sensitivities were 2.0659 × 105 nm/RIU in the RI range of 1.3330∼1.3741 and 7.837 nm/ °C at 1080 °C.

A model of laser cooling in a fiber with a doped cladding shows that a radiation-balanced fiber laser (RBFL) made of silica can produce substantial output powers. Bidirectional pumping is found to reduce the average temperature of the laser, enabling higher output powers while maintaining radiation-balanced operation. For a large-mode-area silica fiber doped with Yb in the core and cladding, simulations predict that output powers as large as 115 W can be achieved by bidirectionally pumping the doped cladding. This is not only slightly higher than with a Yb-doped ZBLAN fiber with the same dimensions, but the temperature gradient in silica is also about half as large. Since silica is the most common host in fiber lasers, these predictions are very promising for the near-term realization of practical RBFLs.

We present the development of an As2S3 fiber-based reusable inline optical connector; and, for the first time to the best of our knowledge, integrated it into a 2 μm chirped pulse amplification system as the pulse stretcher. By this mechanism, a near 20 times pulse stretching ratio was achieved in 0.5 m-long this As2S3 fiber and the introduction of insertion loss as low as 2.84 dB while it was connected with silica fiber. After the follow-up fiber amplification and self-compression mechanism, the laser average output power was boosted to 1.97 W and pulse duration was optimized to 2.53 ps. Moreover, to further inspect the laser pulse property, the pulses were then delivered into a 5.3 m-long ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber which was fusion spliced to SM1950 fiber. Thanks to the 0.4-dB low fusion splice loss between these fibers, a 1.56-W supercontinuum source with bandwidth of 1.93-3.50 μm is obtained. The measured two hours of root-mean-square value of power fluctuation of this laser source is 0.13%, indicating an ultra-high long-term power stability. This work will lay a solid foundation in the realization of the all-fiber structured high-power thulium-doped fiber amplifier with high compactness.

An ultracompact optical fiber temperature sensor with a fiber-tip structure is proposed and demonstrated based on the Fabry–Perot (FP) interference principle. Composing a tellurite glass microcavity and a commercial multimode fiber, the proposed sensor is fabricated using a simple method of dipping. The theoretical analysis and experimental observation demonstrate that the ambient temperature can be detected by monitoring the wavelength shift of the reflection spectrum. The obtained sensitivity is about 62 pm/°C with linearity of 0.99982 in the range of 20 °C–170 °C. This sensor has great fringe contrast, high linearity, good stability, a wide detection range, and a short response time. It avoids the fusion difficulty between tellurite fiber and silica fiber, and provides a possibility for real-time temperature detection in the biological field and harsh industrial environment.

Room-temperature-curable, easy to fabricate, low-cost epoxy novolac composites, reinforced with silica fiber were investigated as ablative thermal protection systems for moderate thermal environments. These composites possessing good mechanical and thermo-mechanical properties were prepared by blending epoxy novolac resin with the reinforcement and varying proportions of glass microballoons (1, 3, 5, and 10% by wt). The composites were cured using polyamidoimidazoline. Complete curing of the epoxy groups was ensured from Fourier transform infra-red spectroscopy (FTIR) and Differential scanning calorimetry (DSC), while the extent of cure was monitored by rheometry. The composites exhibited inter laminar shear strength > 23 MPa and flexural strength > 120 MPa. The thermal and thermo-oxidative stability were monitored by thermo-gravimetric analysis (TGA). The composites were found to be self-extinguishing with Limiting Oxygen Indices (LOI) in the range of 40–46%. Coefficient of thermal expansion (CTE) and specific heat were in the range of 4.8–7.0 × 10–6/°C and 0.6–0.64 cal/g/°C respectively. The composites exhibited heat of ablation in the range of 1.4–1.7 × 107 J/kg which renders them potential candidates for ablative applications capable of withstanding moderate heat flux applications.

Sensing performance of silica fiber Bragg grating (FBG) and chalcogenide FBG are compared in presence of apodization functions. The Bessel and Gaussian apodization functions are chosen in this analysis. These fibers are compared on the basis of their sensitivity, detection accuracy, quality parameter and sidelobe suppression ability. Reflectivity equations established from couple modes equations by matching fields at interfaces. For considered apodization profiles, it is observed that the sidelobe suppression ability and sensitivities are nearly same in both chalcogenide and silica fiber Bragg grating. Chalcogenide-based fiber Bragg grating with Bessel apodization function have narrower full width half maxima (FWHM) value that’s why its detection accuracy and quality parameter is maximum in comparison of other considered cases. Hence for sensing application purpose chalcogenide-based fiber Bragg grating in presence of Bessel apodization function is appropriate.

We present a one-step fabrication method for a new multiplexed electrospray emitter with nine parallel micronozzles. The nozzles were formed by wet chemical etching of the end of a microstructured silica fiber containing nine 10 μm flow channels. By carefully adjusting the water flow through the channels while etching, we controlled the shape of the conical micronozzles and were able to obtain conditions under which the micronozzles, together with the flow channels, formed optical micro-axicon lenses. When 1064 nm light was guided through the flow channels and focused by the micro-axicon lenses into the Taylor cones, we were able to increase the desolvation of a model analyte and thereby increased the spray current produced by the emitter. This work paves the way towards a rapidly modulated mass-spectrometry source having a greatly enhanced throughput.

In this paper, we propose and design a Ge-doped air-core ring fiber, which can support a large amount of OAM modes for mode-division multiplexing (MDM) in optical fiber communications. By varying the mole fraction of GeO2 and adjusting the structure parameter, including the air-core radius and the GeO2-doped ring width, we investigate the influence of different fiber parameters on the total supported OAM mode number. The hollow silica fiber with a 50- $\mu \text{m}$ air core and a 1.5- $\mu \text{m}$ thickness of Ge-doped ring is designed in simulation to support fiber eigenmodes up to HE112,1 and EH107,1. This provides 436 OAM modes at 1550 nm while maintaining radially single mode condition. Moreover, it can support more than 400 radially fundamental OAM modes for the wavelength from 1460 nm to 1625 nm, covering entire S, C and L bands. The optical parameters of the guided OAM modes in the fiber are also numerically analyzed, including effect of material loss, optical field distribution, effective refractive index profile and chromatic dispersion, etc. The simulation results show that the higher-order OAM modes have longer $2\pi $ and 10-ps walk-off length in the air-core ring fiber with ellipticity or bending compared with low-order modes.

To increase bandwidth and number of channels per fiber for more than one wavelength in the same fiber the dense wavelength division multiplexing (DWDM) technology has been utilized. One of the devices that are important in DWDM is an optical interleaver. This paper discussed the effects of temperatures in the DWDM interleaver by using the Mach-Zehnder interferometer (MZI) structures which is arranged in two-stage cascaded MZI and the three-stage cascaded MZI geometries. The main consequences of increase temperature inside the fiber optics are the change of effective refractive index in the material of silica fiber due to the thermo-optics effects. In our analysis we have used the transfer matrix method to investigate the wavelength dependence of output power to the temperatures changes that varies from 30oC to 430ºC. In the calculation we have used the C-Band range wavelength which is around 1530 to 1565 nm. It has been shown that the change of temperatures may shift the wavelength inside the MZI output power in linear manners. These effects may be used to tune wavelength transmission inside the MZI structures to suit the ITU-T defined grid.

International audience; Rare Earth Elements-doped glasses have applications in many fields, and for example, Al and Ce codoping in silica optical fibers is usually done to attenuate the optical degradation (photodarkening) of, e.g. Yb and Tm doped silica optical fibers. To shed some light on the effect of codoping on the optical properties and the glass structure of SiO 2 fibers, we investigated a SiO 2 fiber preform having a gradual increase of the CeO 2 + Al 2 O 3 content from 1.5 to 6.3 mol% and a CeO 2 /Al 2 O 3 molar ratio varying from 0.04 to 1.4. Raman and photo-luminescence spectroscopies have been used to evaluate changes in the short-and medium-range order both in the cladding and in the core portions, and the evolution of the glass optical properties, respectively. The variations of the excitation and emission have been linked to modifications in the vibration bands of the Raman spectra, and in turn, the relationship between optical properties and glass connectivity has been carefully considered. Our results show that there is a strong positive linear relationship between the increase of the Raman bands in the high-frequency range and the red-shift of the excitation maxima. Therefore, the change of < Ce-O > distances and bond covalency character influences, in the same way, both the photoluminescence behavior of the core and the connectivity of the amorphous network.

Passive treatment systems provide lower cost alternatives for remediation of mine drainage; however, acidic drainage increases treatment difficulty because of higher metal concentrations and proton competition for reactive substrates. A silica fiber functionalized with (3-aminopropyl) triethoxysilane (Si + APTES) and a naturally-occurring, microporous silicate mineral (clinoptilolite of the zeolite family) were evaluated in the laboratory as potential reactive substrates for passive treatment of mild (≥ pH of 3) acid rock drainage. Column permeability experiments with spun, 10-µm median diameter, silica fiber and loosely packed, 3.6-mm median diameter clinoptilolite indicate greater permeability and stability of clinoptilolite under flowing conditions. Batch sorption experiments with silica fiber (Si), Si + APTES, and clinoptilolite in a synthetic Fe(II)–SO4, pH 3.0 solution indicate an Fe specific sorption efficacy of Si + APTES > clinoptilolite > Si at equivalent surface areas. Specific sorption normalized to packing densities indicate greater sorption per volume for clinoptilolite. Sorption results for Si + APTES and clinoptilolite did not produce isotherms described by the Langmuir or Freundlich models, likely because of surface heterogeneity and precipitation reactions. Column sorption experiments under flowing conditions indicate an Fe removal efficacy of clinoptilolite > Si + APTES for permeable packing densities. Si + APTES demonstrated high specific sorption of Fe in batch sorption experiments and has potential use in low-flow, passive treatment of mildly acidic solutions. The balance of minimal surface preparation, greater permeability, structural stability, large surface area, micropore structure, and ion-exchange properties make clinoptilolite a better reactive substrate for passive treatment of mildly acidic solutions in high- or low-flow conditions.

The operation of the Ytterbium (Yb)-doped silica fiber laser is investigated under high temperature gradients generated by various cryogenic materials. A continuous-wave (CW) double-clad single-mode fiber laser working at 1082.51 nm with a linewidth (FWHM) of 0.16 nm and an average power of 10 W was used to study the effect of cooling rate on its output characteristics such as signal power, efficiency, central wavelength and spectral bandwidth. The cooling process is performed along the gain fiber using a cryogenic bath, while the cryo-coolants don't touch other laser components such as fiber Bragg gratings (FBGs), combiners and optical couplers. A series of rigorous experiments are carried out at room temperature - RT (22.5 °C) and cryo-states when the gain fiber is immersed in different coolants i.e., dry-ice ethylene-glycol - DIEG slurry (-29 °C), dry-ice debris (-58 °C) and liquid nitrogen - LN2 (-189.2 °C) with various pump powers ranging 2.9 - 16.5 W. The gain fiber of 10 m long demonstrates a 36 % power efficiency at LN2 against 66.4 % at RT. The signal power as well as the laser efficiency linearly reduces with temperature drop as to the linewidth undergoes a lucid spectral narrowing accompanying blue shift, mainly owing to the notable temperature response of the absorption / emission cross-section, broadening mechanisms and thermal population as well as energy level schemes, including sublevel and hyperfine structures of the transition accordingly.

A 20.6-W mid-infrared supercontinuum (MIR-SC) generation is demonstrated in a piece of step-index ZBLAN (ZrF4−BaF2−LaF3−AlF3−NaF) fiber. A silica-fiber-based SC laser operating at 1.9–2.6 μm is used as a pump source. Owing to the specially designed ZBLAN fiber which perfectly matches the pigtail of the pump source in mode-field-diameter, direct fusion splicing was achieved between the ZBLAN fiber and the pigtail of the pump source instead of being connected via a piece of transition fiber. The coupling loss of the fusion splicing joint between the silica fiber and the ZBLAN fiber was measured as 0.26 dB@2000 nm. Robust fiber endcap made of multimode AlF3 fiber also benefited high-power MIR-SC generation. Spectral and power characteristics of the generated SC under different pump pulse duration and pulse repetition rate were carefully studied. A 20.6-W SC was obtained with an overall spectral coverage and a 10-dB long wavelength edge of 1.92–4.29 μm and 4.08 μm, respectively. This is, to the best of the authors’ knowledge, the first demonstration of 20-W level SC laser based on ZBLAN fiber with long wavelength edge extending beyond 4 μm.

The rectangular-structured resin with one of its triangular long-period fiber grating surface is designed and printed out by using a high resolution 3D printer, so called long-period fiber grating (LPFG) resin. This LPFG resin is directly pressed on the bare single-mode fiber by a digital force meter to filter out partial band of light inside the fiber. The grating period is expanded by tilting the resin from the initial fiber axis. The optical filter is observed as resonant wavelengths from the broadband wavelength. The results show that the resonant wavelength shift is a linear function of the grating period with the coefficient of determination over 0.99. The proposed scheme has a great potential to be employed as a sensor such as a selective optical filter and a buried intrusion sensor.

The development of superabsorbent materials with high absorption capacity, selectivity, and stable performance is needed for oil recovery. Remote-controlled oil absorption is highly favorable for oil absorption in harsh environment. In this study, a novel ultralight superhydrophobic nanocomposite aerogel composed of organic cellulose nanofibrils (CNFs), inorganic silica fiber, and magnetic Fe3O4 nanoparticles was developed through a simple freeze drying and surface modification method as a magnetically driven superabsorbent material. The aerogel has a highly porous and fibrous structure that contains hierarchical micro-nano surface topography. Low surface energy carbon–fluorine chains were grafted on aerogel surface which rendered the aerogel superhydrophobic. The addition of Fe3O4 nanoparticles significantly improved the surface area, compressive property, water contact angle, and the separation efficiency of the aerogel, but reduced the absorption capacity due to the increase of bulk density. The developed nanocomposite aerogel has a high absorption capacity (weight gain of 3420–5837%), separation efficiency ~ 100%, and a water contact angle of 150°. It also demonstrated high elasticity and performance stability in repetitive use. Given its magnetic property, the CNF/silica/Fe3O4 nanocomposite aerogel is a promising candidate for selective oil removal from open water, especially for remotely controlled applications.

We report the experimental performance of a packaged dual-stage all-single-clad broadband polarization maintaining (PM) Tm-doped silica fiber amplifier (TDFA) with a high signal output power of 2.2 W at 1909 and 1951 nm. Our novel design incorporates an uncooled 940 nm multimode semiconductor pump laser source. Combined high gain of >46 dB, wide operating bandwidth of 1875-2000 nm, low noise figure of 7 dB, high OSNR of >54 dB/0.1 nm, and a PER of >20 dB are achieved with our TDFA.

Silica optical fibers (OF) having a core diameter of 400 – 800 μm made of biocompatible materials are widely used in laser medicine. The results of studying the optical parameters of novel silica-polymeric optical fiber with a reflective thermoplastic copolymer coating (tetrafluoroethylene – ethylene) and the influence of coating conditions on these optical parameters are presented. Coatings from polymer melt were applied to the silica fiber surface by orifice drawing. The numerical aperture of the drawn OF was measured by distribution of the laser radiation emerging from OF in the far field. The optical losses were determined by the distribution of the radiation scattered by the reflective coating along the OF length. The scattering parameters of the laser radiation transmitted through OF were estimated by the intensity and indicatrix of scattering. We studied OF samples up to 50 m in length with a silica core of about 400 μm in diameter and reflective coating with a thickness of 70 – 90 μm, the reflective coating also performed a protective function. The quality of applied coating and optical parameters of the OF samples depended on the speed of fiber drawing (coating speed) Vd. A smooth coating was obtained at Vd ≤ 2 m/min. When Vd > 2 m/min the coating became rough, turning into the so-called «shark skin» at Vd = 6 m/min. Observed scattering of radiation passing through the studied OF samples was attributed to the polymer structure which contained both crystalline and amorphous phases with different values of the refractive index. The smallest scattering was observed in a smooth-coated OF. The total optical loss at a wavelength λ = 532 nm amounted to 300 – 720 dB/km (a nominal numerical aperture was 0.44). Short (1.5 – 3 m) OF samples were shown to provide a transmission of 80 – 93% of the input power.

A kHz-linewidth single-frequency laser at 1070 nm was demonstrated based on homemade heavily Yb3+-doped Yb:YAG-derived silica fiber (YDSF), which was fabricated by molten-core fabrication method. Stable single-longitudinal-mode (SLM) lasing operation was achieved by adopting ring cavity configuration, where a piece of un-pumped polarization maintaining Yb3+-doped fiber (PM-YDF) was utilized as a saturable absorber (SA). A maximum output power of the stable single longitudinal mode continuous wave laser up to 40 mW was obtained with a pump power of 542 mW at 976 nm. The optical signal-to-noise ratio (OSNR) was ~60 dB, and the laser linewidth was measured to be less than 4.3 kHz, which is limited by the measurement setup. The fluctuation of center wavelength of the laser was less than 0.1 pm within 10 min. Wavelength tuning from 1069.99 to 1070.42 nm was achieved by controlling the temperature of the fiber Bragg grating (FBG).

We report the basic spectroscopic properties of a home-made holmium-aluminum-germanium co-doped silica fiber, designed for laser applications. We present the ground-state and excited-state absorpti...

We have proposed a very advanced super dense wavelength division multiplexing (SD-WDM) system using RAMANErbium doped silica fiber optical amplifier (EDSFA) hybrid optical amplifier (HOA) in this paper. Performance is evaluated in term of flattened gain and noise figure for C-band. Effect of proposed hybrid optical amplifier also compared with EDFARAMAN, EDFA-SOA and SOA-SOA HOA for the same characteristics. Best rating gain of 37.5 dB with noise figure of 5.4 dB ever recorded from RAMAN-EDSFA HOA. It is also observed that out come from SOA-SOA HOA is not acceptable in term of noise figure of 9.1 dB for 400 x 10 GB/s SD-WDM system. Keywords: SD-WDM, RAMAN-EDSFA, EDFA-RAMAN, EDFA-SOA, SOA-SOA, noise figure, gain

Author(s): Cheng, S; Song, C; Ercius, P | Abstract: To investigate the possible structural differences between silica glass fibers and bulk silica glasses, electron energy loss spectroscopy (EELS) has been used to study the short-range and medium-range structures of both forms of silica glasses. The short-range structure of silica glass, such as the coordination and symmetry, was investigated by the energy loss near edge structure (ELNES) of Si L2,3-edges. The ordering structure in the medium-range was analyzed by the exponential optical absorption edge also known as the Urbach edge of the glasses. The optical absorption data were obtained from the low energy loss spectrum of EELS through Kramers-Kronig analysis. The results show that silica fiber has the same short-range structure as the bulk specimen, but is significantly more disordered than the bulk glasses.

We demonstrate selective excitation and coherent amplification in the multicore fiber of the out-of-phase supermode that has equal intensities but interleaved 0/π phases in the neighboring cores. The out-of-phase supermode is beneficial due to its stability at arbitrary high powers, whereas the fundamental supermode becomes unstable at relatively high powers. We fabricated a double-clad all solid silica fiber with six highly Yb-doped coupled cores arranged in a ring structure. We obtained amplification of 50 picosecond chirped pulses up to ∼1 μJ energy with measured content of the out-of-phase mode of >80%. The experimental results were supported by 3D numerical simulation demonstrating the possibility of the out-of-phase supermode amplification in the multicore fibers with real parameters without degradation of supermode composition for powers up to damage threshold in silica glass.

The spectroscopic properties of Er3+-doped tellurite glasses were investigated and a 1 wt.% Er3+-doped tellurite fiber was fabricated for L-band lasers. Wavelength-tunable fiber lasers in a linear cavity based on Littrow configuration were developed and studied with different gain fiber lengths as well as output coupling ratios. Wavelength tunable range of 38 nm from 1589–1627 nm was achieved in the experiment with a 3-m Er3+-doped tellurite fiber laser pumped at 1570 nm. A maximum output power of 52.4 mW was obtained at 1614 nm. Compared to L-band Er3+-doped silica fiber lasers, the demonstrated Er3+-doped tellurite fiber lasers exhibit much higher optical signal-to-noise ratio (>30 dB), even at the longest operating wavelength of 1627 nm. Our simulation shows that the laser wavelength can be further extended to 1634 nm if the tellurite fiber loss is improved and the fiber cavity is optimized.

Similar to components in electronics industry, optical systems are also increasingly miniaturized. The integration of functions as well as the production of optical freeform surfaces, which are not manufactural with conventional manufacturing processes, are of special interest. One method for additive manufacturing of glass components is the Laser Glass Deposition (LGD) by using a CO2 laser source (10.6 µm). This allows printing functional waveguides in individual shapes. The process is also able to generate spheres for e.g. a planar lens matrix. In this paper the reproducible controlled deposition of spheres using a fused silica fiber with a diameter of 400 µm is investigated. For this purpose, a parameter variation of the fiber feeding speed and laser power is carried out to produce spheres of different sizes and in different arrangements. Finally, the optical and stress-mechanical properties of the samples are investigated.

We report the development of a silica glass single-mode polarization-maintaining fiber with birefringence induced by artificial anisotropic glass in the circular core without any external stress zones or structured cladding. The fiber core is composed of silica and germanium-doped silica nanorods ordered in submicrometer interleaved layers. The fiber has a measured cut-off wavelength at 1113 nm, phase birefringence of 0.3×10−4, and an effective mode diameter of 10.5 µm at the wavelength of 1550 nm. The polarization extinction ratio in the fiber is 20 dB at 1550 nm. The fiber is compatible with the standard SMF-28 fiber and can be easily integrated using standard fusion splicing with losses of 0.1 dB.

We demonstrated a biocompatible and highly sensitive temperature sensor using DNA-CTMA (DNA-Cetyl trimethyl ammonium) solid film deposited on micro-tapered fiber. The micro-tapered silica fiber provided a built-in interferometer that was inherently sensitive to the environment variation due to the enhancement of evanescent wave interaction. The tapered region was coated with DNA-CTMA film with a high thermo-optic coefficient enabling a high-temperature sensitivity higher than −0.9 nm/°C in the bio-medically important region from 35 to 80 °C in a water bath. The cross-sensitivity problem between the temperature-sensing and the strain-sensing was successfully resolved since the elastic properties of the DNA-CTMA film on the micro-tapered silica fiber resulted in a very low strain sensitivity of −7 pm/ $\mu \varepsilon $ . Detailed procedures for device fabrication and optical characterization of the proposed device were described.

Erbium-doped fiber amplifiers are used for amplifying optical signals. In this type of optical amplifier, the core of a silica fiber is doped with Er3+ ions. Here, the effects of temperature on the gain parameters for short-length erbiumdoped fiber amplifiers are simulated. Temperatures were selected over a wide range (−200 to +80°C) for different ion densities to simulate extreme conditions, such as the presence of liquid nitrogen. The maximum gain occurs at temperatures close to 0°C, and the Er3+ concentration also plays an important role.

In this work, a compact all-fiber bend sensor based on a dual-core microstructured optical fiber has been manufactured and characterized. The sensor relies on the unbalanced Michelson interferometric technique realized by attaching a piece of silica fiber to one of the fiber cores acting as the unbalancing element. Three probes with different lengths of the unbalancing element have been experimentally tested for sensitivity tailoring analysis. Additionally, a theoretical model has been developed for comparison and verification of the results. Good linear behavior of the spectral shift with bend has been measured and it has been proven that the sensitivity of the sensor depends on the length of the unbalancing element and the orientation of the cores. Higher sensitivities are achieved for shorter lengths of the unbalancing element and orientation of the core axis parallel to the bend direction. The highest sensitivity reported is 9.97 pm/µm for the case of 34 µm of unbalancing element and orientation of 0 degrees.

International audience; We demonstrate the use of a dysprosium-doped silica fiber saturable absorber in a passively Q-switched erbium-doped fluoride fiber laser operating at 2.8 µm.; Nous mettons en évidence l'utilisation d'un absorbeur saturable en fibre de silice dopée au dysprosium dans un laser à fibre au fluorure dopé à l'erbium à commutation passive fonctionnant à 2,8 µm.

The high accuracy fitting of the Raman gain profile is presented using two independent methods, namely the multimode Gaussian decomposition and rational approximation. The accurate approximation of experimental data was resulted in a simple analytic form and it is forming the reliable basis for calculating a lot of the mainly important practical parameters for many devices based on Raman photonics.

A novel PbS/PbSe co-doped fiber is fabricated by the modified chemical vapor deposition (MCVD) technology. Its absorption and luminescence characteristics are investigated. There are two absorption peaks at 773 and 1161 nm, respectively. The luminescence spectrum ranges from 1000 to 1350 nm. In addition, the intensity of luminescence is related to pump power.

The magneto-refractive characteristics of erbium-doped silica fiber (EDF) are of great significance in magnetic field sensing. The fiber doped with rare earth Er3+ has a large magnetic moment and spin splitting, which makes a major contribution to the magnetic properties of the fiber. The refractive index of EDF in different magnetic fields was measured. The experimental results show that the refractive index of EDF decreases linearly with the increase of magnetic field. The magneto-refractive sensitivity of EDF is 3.21×10−5 RI /mT, which is about 20 times higher than that of single-mode fiber. The magneto-refractive properties of silica fiber are enhanced by rare earth element Er3+.

We report on the feasibility of short-wavelength transmission window modification in anti-resonant hollow core fibers using post-processing by hydrofluoric (HF) acid etching. Direct drawing of stacked anti-resonant hollow core fibers with sub-micron thin cladding capillary membranes is technologically challenging, but so far this has been the only proven method of assuring over an octave-spanning transmission windows across the visible and UV wavelengths. In this study we revealed that low HF concentration allows us to reduce the thickness of the cladding capillary membranes from the initial 760 nm down to 180 nm in a controlled process. The glass etching rates have been established for different HF concentrations within a range non-destructive to the anti-resonant cladding structure. Etching resulted in spectral blue-shifting and broadening of anti-resonant transmission windows in all tested fiber samples with lengths between 15 cm and 75 cm. Spectrally continuous transmission, extending from around 200 nm to 650 nm was recorded in 75 cm long fibers with cladding membranes etched down to thickness of 180 nm. The experiment allowed us to verify the applicability and feasibility of controlling a silica fiber post-processing technique, aimed at broadening of anti-resonant transmission windows in hollow core fibers. A practical application of the processed fiber samples is demonstrated with their simple butt-coupling to light-emitting diodes centered at various ultraviolet wavelengths between 265 nm and 365 nm.

Pulsed laser sources in the spectral window of 2 μm find many applications in engineering and science [1] . Thulium doped fiber lasers (TDFL) are especially attractive for this purpose with their emission in the 1.8-2.1 µm spectral range. The emission spectrum of a TDFL beyond 2.1 µm is also attainable with nonlinear approaches such as soliton self-frequency shift (SSFS) [2] , [3] . Previously, TDFL systems using SSFS have been demonstrated from thulium-doped fiber amplifiers (TDFA) pumped by tens of watts of continuous wave signal, leading to high-power femtosecond pulses (~100 kW, ~100 fs) [4] , [5] . However, such high-power systems are bulky and require external cooling mechanisms, as well as they lead to SSFS for a specific wavelength and pulse intensity. On the other hand, reports of TDFL with SSFS from passive fibers such as Ge-doped fibers require custom-made dispersion engineered fibers [6] . Here, we present a simple, all-fiber system that extends the wavelength reach of a TDFL from a passive, commercially available silica fiber. The system is tunable over 310 nm with an energy conversion efficiency up to 84.6%. To the best of our knowledge, this is the highest energy conversion efficiency ever reported in any SSFS system based on a passive fiber.

Fiber lasers emitting at wavelengths around 2 μm in continuous wave (CW) regime are promising sources of laser radiation for both civil (surgery, spectroscopy, lidar) and military applications as infrared countermeasures or laser weapons [1] . Optimizing the size, weight and power of lasers devoted to military activities is a major concern. The need of high power compact and robust laser sources leads us towards all-fiber solutions by using a single-oscillator architecture. In this contribution, we present a high power monolithic fiber laser source based on a Tm 3+ , Ho 3+ -codoped silica fiber emitting at around 2 µm in CW regime.

A broadband supercontinuum is generated from a thulium ultrafast soliton fiber laser in a high numerical aperture silica fiber with low nJ seed pulse energies. Amplification of a thulium based ultrafast soliton ring fiber laser in two customized thulium doped fiber amplifiers provides pulses varying in energy between 1.8 nJ and 13.5 nJ. Coupling these seed pulses into a high numerical aperture silica fiber UHNA 7 of varying length, a systematic study of the impact of pulse energy, pulse duration and nonlinear fiber length is conducted. Based on the normal dispersion, self-phase modulation dominates for lower pump power values and results in a symmetric spectral broadening process. For higher pulse energies, four-wave mixing and Raman scattering contribute to a strong red-shift of the spectrum beyond 2.3 μm. For a fiber length of 20 m of UHNA 7, a broadband supercontinuum spanning from 1.7 μm to 2.33 μm is generated with a 20 dB spectral bandwidth of 502 nm with an output pulse energy of 4.4 nJ, corresponding to an output power of 92 mW. This represents a low seed energy threshold for efficient flat supercontinuum generation at infrared wavelengths.

A homemade 25/400 thulium-doped silica fiber for high power laser and an all-fiber bi-direction pumped thulium-doped master-oscillator power-amplifier (MOPA) configuration with output power of 406 W are presented. The concentration of Tm 2 O 3 and Al 2 O 3 was set as 2.6 wt.% and 1.01 wt.% respectively. Cladding Absorption at 793 nm was measured to be 3 dB/m. The output power of 406 W was obtained by improving coating stripping of splice for thermal management, corresponding to slope efficiency of 54%. The 3 dB spectral linewidth was narrow as 84 pm. Neither amplified spontaneous emission (ASE) nor non-linear effect was observed and the output power only limited by pump power.

We demonstrate a novel fiber Bragg grating (FBG) temperature sensor based on lead sulfide (PbS)-doped silica optical fiber, prepared by atomic layer deposition (ALD) doping technique. The FBGs are fabricated using the phase mask method, without hydrogen loading. The temperature sensitivity of the FBG-PbS is found to be $\sim$ 19 pm/ $^\circ$ C within 20–150 $^\circ$ C, showing great linearity and repeatability. It is increased by approximately 60% compared to the temperature sensitivity of FBG in standard single mode fiber (SMF). Furthermore, the temperature characteristics of PbS-doped silica optical fiber are investigated. The thermal expansion coefficient and thermal-optic coefficient of PbS-doped silica fiber are 6.3 $\times\; 10^{-7}$ and 1.23 $\times\; 10^{-5}$ / $^\circ$ C, respectively. Moreover, the thermal-optic coefficient value of the PbS-doped silica optical fiber is nearly one order of magnitude higher than that of SMF. Therefore, the FBG based on PbS-doped silica optical fiber appears to be very attractive for the temperature sensing fields.

Long-period gratings (LPGs) induced in optical fibers show exceptional refractive index (RI) sensitivity and thus they are often applied for label-free biosensing. However, during measurements at changing environmental conditions, the surface of the fiber made of fused silica is subjected to stresses that can cause alterations in its structure. The problem is particularly important when long-term or biosensing measurements are considered and when sensor surface may be exposed to subsequent drying and immersion in aqueous solutions. The aim of this paper was to investigate the influence of sequential drying in air and soaking in water of the fused silica fiber cladding surface on the optical response of LPGs. We demonstrated that transmission spectrum of LPG measured in water before and after drying in air differed significantly and further changed with subsequent drying steps indicating increase of the local RI. All these changes correspond to the alterations in the cladding surface, i.e., its fracturing and pores rearrangement, caused by the stress induced during drying and then immersing in water, as well as possible corrosion and formation of nanosized objects on the cladding surface. The effect can be additionally influenced by washing the samples in organic solvents. We confirmed that measurements done in a flow-cell system, where the sensor was kept wet during the sensing experiment may eliminate the water-induced fiber surface alteration effect and thus minimize the amount of false results. Described findings are highly important for biosensing applications of any optical-fiber-based devices.

The authors present here an attainable fiber supercontinuum source with competitive characteristics in the near infrared range. The proposed system is based on a highly nonlinear silica fiber, with nominal zero-dispersion wavelength at 1550 nm. A mode-locked fiber laser was used as the seed. The pump wavelength was shifted to match the zero-dispersion wavelength of the nonlinear fiber, achieving a better performance of the spectral emission. The supercontinuum emission was characterized between 1100 nm and 2300 nm, showing a flat and wide spectrum with a conversion efficiency over 80%. The set-up consists only in silica fiber and can be considered, therefore, as a cost-effective alternative for supercontinuum generation in the near infrared range, which can be easily implemented in any photonics laboratory, where commercial amplifiers are usual devices.

A hydrophobic coating of the silica fiber reinforced silica composites (SiO2f/SiO2) was synthesized by sol-gel method using methyltriethoxy-silane (MTES) and boric acid (B(OH)3) as raw materials. The relationship among boron doping, chemical structure of precursors and durability of hydrophobic coatings was discussed. The Si-O-B and methyl groups were successfully introduced in the gel precursors according to the FT-IR and XPS results. The resins were filled in the internal and surface holes of the SiO2f/SiO2 composites partially or completely, which is beneficial to reduce the physical adsorption of the moisture. In addition, hydroxyl groups of the SiO2f/SiO2 composites reacted with the resins and hydrophobic methyl groups were introduced, leading to the reduction of the chemical adsorption of water. Also, the boron doping was beneficial to enhancing the physical cross-linking between the coating and the SiO2f/SiO2 composites, and improved the adhesion of the coating to the substrate. The results show that the optimal hydrophobic coating with contact angle 130.33°, moisture absorption 0.33% and adhesion level 1 is obtained when the molar ratio of MTES to B(OH)3 is 10:4. The real permittivity of M10B4 is constant in the range of 2.32–2.51 and the dielectric tangent loss is constant in the range of 5.5 × 10−4–8.7 × 10−3. The hydrophobic coating has excellent dielectric properties. Keywords: Adhesion, Dielectric, Hydrophobic, Polyborosiloxane, SiO2f/SiO2 composites

The thermal stability of drawing-tower grating (DTG) has become the primary concern in applications because of its great advantages in building a large-capacity distributed fiber grating sensing network. Different aging trainings were performed on the DTGs written by single laser pulses at 193 nm in a low-germanium doped silica fiber, and the thermal stability of Bragg wavelength and reflectivity at different temperatures were investigated to demonstrate that the DTG is reliable in some sensing applications. A double exponential function model is proposed as a method to study the decay characteristics of the DTG reflectivity.

Type I and type II Bragg grating arrays in silica fiber have been irradiated at the Ohio State University Nuclear Reactor Laboratory in the gamma facility and the pool-type reactor, to receive a relatively small gamma dose (2.82 Mrad) and a relatively large gamma–neutron dose (638 Mrad, ${6\times }{10}^{17}\rm {({n}/{cm^{2}})}$ ), respectively. The Bragg grating fibers were first irradiated in the gamma facility and those same fibers were then subsequently irradiated in the reactor, while being monitored in situ by optical frequency domain reflectometry. The response of the Bragg gratings, in terms of reflected amplitude, was analyzed, both in the frequency and spatial domains. A Bragg grating modeling code, written in MATLAB, was then used to generate modeled fiber Bragg grating (FBG) responses to match the experimental responses, based on some fundamental assumptions. With the modeled responses, we were able to deduce the alterations to the refractive index profile of the Bragg grating inscribed fibers as a result of the irradiation.

Interest in polymer optical fiber Bragg gratings (POFBGs) arises from the different material properties and sensing modalities brought by polymers relative to silica. Polymer fibers typically offer twice the sensitivity to temperature of conventional silica fiber and increased sensitivity to strain overall. In addition, polymer fibers have higher elastic limits and as a result a larger range of operation for physical constraints. While some polymers are effectively humidity insensitive, others present inherent humidity sensitivity. Their organic properties also allow a variety of chemical processes to create (bio)chemical sensors, with the consequences of fiber breakage in situ being less hazardous than silica. These attributes have led to the use of POFBGs for applications that remain complex using silica fibers. This review paper covers the progress toward commercialization and the increasing number of specific applications.

In this paper, a single-frequency thulium-doped silica fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode (SMS) structures incorporating a Sagnac loop was experimentally demonstrated. Based on the analysis of the transmission properties of the SMS fiber structure and the mode selection characteristic of the Sagnac loop, two cascaded SMS fiber devices with the same multimode fiber length of approximately 3.25 cm were used in our laser system, to select the specific lasing wavelength above 2 μm, as well as enhance the suppression of lasing around 1900 nm. A 6.5-m-long unpumped thulium-doped silica fiber was employed in the Sagnac loop as a saturable absorber to achieve single-longitudinal-mode operation. Single-frequency operation of the fiber laser at 2004.9 nm has been achieved with a maximum output power of 20.9 mW.